Currently, internal combustion engines for vehicles have varied specifications such as a length, an installing orientation and a connector's orientation. Some stick ignition coils have two housings separately formed from each other for enclosing a coil and an igniter to adapt themselves to the varied specifications of the engines
US-6,781,500-B2 and US-2004/0104796-A1 (JP-2003-303724-A) discloses an ignition coil, as shown in FIG. 9, that has a first housing 150 and a second housing 155. The first housing encloses a center core 151, a primary coil 152, a secondary coil 153, etc. therein. The second housing 155 encloses an igniter 156, a terminal 157, etc. therein. The second housing 155 has a cylinder-shaped fitting portion 155a fitted to an outer circumferential face of a cylinder-shaped cylinder top portion 150a of the first housing 150. Insulating resin 161, 162 fills gaps between the center core 151, the primary coil 152 and the secondary coil 153 in the first housing 150 and a cavity around the igniter 156 in the second housing 156.
To assemble the first housing 150 and the second housing 155 into the ignition coil, an inner circumferential face of the fitting portion 155a of the second housing 155 is press-fitted to the outer circumferential face of the cylinder top portion 150a of the first housing 150, and the primary coil 152 and the secondary coil 153 are electrically connected to the igniter 156, etc. Then, liquid epoxy resin is charged into the second housing 155 to fill the gaps between the center core 151, the primary coil 152 and the secondary coil 153 in the first housing 150 and the cavity around the igniter 156 in the second housing 156. A heating process cures the liquid epoxy resin charged in the gaps and the cavity.
The above conventional ignition coil, however, has not enough measures against an exfoliation (a crack generation) in the insulating resin 161. The insulating resin 161 suffers a thermal stress in a radial direction of the ignition coil in accordance with the engine's operation. The thermal stress may generate a slight gap between the insulating resin 161 and the top cylindrical portion 150a or between the insulating resin 161 and the fitting portion 155a. Then, the slight gap at a top end of fitting faces of the cylinder top portion 150a and the fitting portion 155a may develop into the exfoliation (the crack) at a adhering faces of the fitting portion 155a and the insulating resin 161.
If the crack extends closer to the igniter 156 and/or the terminal 157 in the second housing 155, the crack may extend into the insulating resin to reach a molding resin of the igniter 156 and/or the terminal 157. As a result, the crack may spoil a function of the igniter 156 and/or break the terminal 157.